You won't find a better selection of high quality solder and flux, copper fittings, and other copper-related products anywhere on the Internet. The acid flux in plumbing solder differs from electrical solder, which contains rosin flux. The strong acid in plumbing solder is very corrosive in order to strip the layer of oxidation off the surface of pipes as the solder melts, allowing it to adhere and form a waterproof joint.